JUBA, May 8 (Reuters) - South Sudanese rebel leader Riek Machar is travelling to Ethiopia and is committed to meeting President Salva Kiir there, his spokesman said on Thursday, the first confirmation that the former deputy president would attend face-to-face talks.

Friday's meeting will be the first time the two men have sat together since conflict erupted more than four months ago. International leaders have put pressure on both sides to meet and prevent ethnic-fuelled fighting from turning into genocide.

Ethiopia is leading the mediation efforts as chair of the regional African grouping IGAD, or the Intergovernmental Authority on Development.

"The agenda will be presented by the mediators, by the teams of the Intergovernmental Authority on Development," Dak said. "We think they will discuss a transitional government, power sharing, but we will wait and see."

Until now, the rebel camp had not publicly stated that Machar would attend the talks.

U.N. Secretary-General Ban Ki-moon said in Juba earlier this week that he had been told by Machar that he would "do his best" to attend, but the rebel leader had also suggested it was difficult to make the journey from his base in the bush.

Kiir told international visitors, who have included U.S. Secretary of State John Kerry, that he was committed to attend.

But his foreign minister, Barnaba Marial Benjamin, also said discussions would be about a "transitional process" not a transitional government, and insisted Kiir would stay on till 2015 elections. Machar has demanded Kiir resign.

Western diplomats involved in the mediation process say the focus on Friday will be on ending violence and implementing a "month of tranquillity", which the two sides agreed to this week, after a ceasefire deal in January swiftly fell apart.

Although they also hope the meeting will start laying the groundwork for a sustainable political solution.

In a sign of the growing frustration at the failure of South Sudan's leaders to end the bloodshed, the United States on Wednesday imposed sanctions on two commanders on opposing sides of the ethnic violence. (Writing by Edmund Blair; Editing by James Macharia)

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